XI 



PHYLUM ARTHROPODA 



597 



FIG. 4S7. Chordotonal (auditory) organ in the tibia 

 of Isopteryx apicalis. 6*, blood corpuscles ; 

 c, integument ; , terminal fibrous strands at- 

 tached to the integument ; gz, nerve cells ; sc. ter- 

 minal rods ; tr. trachea. (From Lang, after v. 

 Graber.) 



Sounds are emitted by many Insects, and are produced by a 

 variety of different means. Often the sound is the result of the 

 rubbing together of opposed rough surfaces of the integument. 

 The chirp of the Grass- 

 hopper, for example, is 

 produced by the rubbing 

 of the femur of the last 

 pair of legs over a series 

 of ridges in the anterior 

 wing, and that of the 

 Locust by the rubbing 

 against one another of the 

 roughened basal parts of 

 the first pair of wings. 

 In other cases the sound 

 results from the rapid 

 vibratory movement of the 

 wings ; this is the case 

 with the buzzing of many 

 Diptera and Hymenoptera. 

 Again, the humming 

 sounds characteristic of 

 many of the last-named 



order are produced partly by the vibrations of the wings in flight, 

 partly by the vibration of leaf-like appendages in the tracheae, set 

 in motion by strong expiratory currents of air. The loud shrill 

 note of the Cicada is produced by the rapidly recurring contractions 

 of the fibres of a muscle inserted into a stiff chitinous membrane, 

 the result being a series of crackling sounds, which follow one 

 another so rapidly as to give rise to a continuous note. 



Reproductive organs. The sexes are always separate in 

 Insects, as in Arthropoda in general ; and the males and females 

 are very commonly distinguishable from one another by various 

 modifications of form and of coloration. There are two ovaries, 

 each of which consists of a greater or smaller number of narrow 

 tubes or ovarioles ; in each of these the ova are arranged in a single 

 row : the early stages in their formation being situated at the 

 anterior end, the more mature ova towards the posterior extremity. 

 Each group of ovarian tubes opens into a lateral oviduct, and the 

 two lateral oviducts, right and left (Fig. 488. A, od.), unite behind 

 to form a median oviduct or vagina (vg.), which opens on the 

 second last segment of the abdomen. Connected with this median 

 oviduct, or opening close to it, are receptacula scminis (rs.) and 

 colleterial or cement glands (sd.). Usually there is a copulatory sac, 

 or bnrsa copulatrix (nva.). In the male the paired testes (B, t.) 

 consists each of one or more long narrow tubes, which, when more 

 than one are present, unite into a vas deferens (B, I'd.), the two 



